Photochemical Synthesis of Phosphinolines from Phosphonium−Iodonium Ylides

We describe three different series of experiments which were undertaken to test our hypothesis that during irradiation of phosphonium−iodonium ylides (1a, 1b) an electrophilic carbene is generated. By opposing the assumed intermediate to monosubstituted alkynes, we observed in the case of electron-rich substituents at the triple bond a domination of a 1,3-dipolar cycloaddition of the intermediate with the triple bond to yield furans. In the case of electron poorer substituents, the formation of phosphinolines prevails. A second series of experiments was carried out with mixed ylides in which one phenyl ring at the triarylphosphonium group was replaced by a thienyl group. In this case, we observe only an intramolecular reaction with the thienyl ring to yield the phosphinolines 21−23. In a third test, we replaced in the mixed ylides 1a, 1b the COR group by a CN substituent. This modification leads to phosphinolines only and avoids a 1,3-dipolar cycloaddition.我们描述了三组独立的实验系列，用以验证我们提出的假说：在对鏻-碘鎓叶立德（phosphonium−iodonium ylides，1a、1b）进行辐照时，会生成亲电卡宾（electrophilic carbene）。通过使该假定中间体与单取代炔烃（monosubstituted alkynes）发生反应，我们观察到：当三键连接富电子取代基时，中间体与三键发生1,3-偶极环加成（1,3-dipolar cycloaddition）反应的路径占据主导，最终生成呋喃类产物。当取代基为缺电子时，磷啉（phosphinolines）的生成成为主导反应路径。第二组实验采用混合叶立德开展，该类叶立德的三芳基鏻（triarylphosphonium）基团上的一个苯环被噻吩基（thienyl group）取代。在此实验条件下，仅观察到中间体与噻吩环发生分子内反应（intramolecular reaction），最终生成磷啉21~23。第三组实验中，我们将混合叶立德1a、1b中的COR基团替换为氰基取代基（CN substituent）。该结构修饰仅会生成磷啉类产物，且完全避免了1,3-偶极环加成反应的发生。